Can an accessory navicular stress fracture lead to flexor hallucis longus tendonitis in a runner? Well, the short answer is yes, and I am going to explain how in today’s episode of the Doc On The Run Podcast.
I was on a consultation call with a runner. She had a very interesting problem. She had a problem called an accessory navicular that developed a stress fracture.
Now, the navicular is this bone right here, and this little bump on the side of it, the navicular tuberosity is different than the body of the navicular over here. And when you get an accessory navicular, it just means that it never fully fused and connected with the rest of the navicular bone as you developed as a child. That’s not a big deal.
However, in her situation, she got a stress fracture in this what looks like an extra piece of bone on the side of the foot, and it hurt. And now that accessory navicular is embedded within the posterior tibial tendon that comes down the back of the tibia and then attaches to the navicular.
There are two other tendons that actually run through the tarsal tunnel. So, the tarsal tunnel is the foot’s equivalent to the carpal tunnel in your hand and the tarsal tunnel has three things in there that are tendons. It has the posterior tibial tendon that attaches to the navicular. It has the flexor hallucis longus tendon that goes all the way down and out to your big toe and helps you push off with your big toe when you run. And then there’s the flexor digitorum longus tendon that goes to the little toes. Does the same thing, but it just spans out to all the little toes.
How can you get tendonitis in something to the big toe when you have a stress fracture in the navicular here? Well, it’s really simple. Here’s the way to think about it. The flexor hallucis longus tendon goes to the big toe. And if you pull the big toe down, you’re firing that tendon. The posterior tibial tendon pulls up on the navicular to help supinate your foot and raise your arch height and tilt your foot over when you’re walking and running.
So, if you get a stress fracture and it hurts right here, or you have posterior tibial tendonitis and it hurts right here, it hurts when you’re firing that tendon around the ankle, well, your body’s going to try to do something to fix it. Your brain’s going to say, okay, well, if we actually pull down real hard with the big toe and push the foot over by firing the flexor hallucis longus tendon, that’ll decrease stress and strain on the posterior tibial tendon and the accessory navicular and that area where the posterior tibial tendon attaches to the navicular.
That’s what was going on with her. She started having all this pain here, started having all these problems. And then as a form of compensation, her big toe was pulling down to forcibly tilt her foot over and decrease stress and strain on the posterior tibial tendon and its attachment all around the stress fracture in her accessory navicular bone. And that is why she started getting problems in the tendon right over her arch that almost seemed like plantar fasciitis, but it wasn’t. It’s above the plantar fascia, it’s up higher, but it’s close.
When she got an MRI, it was evident that she had the fluid in the flexor hallucis longus tendon sheath, as well as fluid around that accessory navicular, where she had this stress fracture. And she had some fluid around the posterior tibial tendon too, where it was also irritated. But these things are usually connected.
If you get one pain in your foot in one area from running, and you have a primary injury that starts first, sometimes you can get a secondary injury that hurts more than the original injury in a different place because something else is getting overused, trying to decrease stress and strain to that thing that got injured the first time.
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